1. Field of the Invention
The present invention concerns a method for the fabrication of a television color tube. It also concerns a front panel for trichromatic television tubes. It can be applied to the reception of high-definition television transmissions.
2. Description of the Prior Art
High-definition television is making it necessary to redefine the fabrication parameters for color television tubes. In particular, the European standard D2-MAC brings the user the following advantages:
plurality of languages in the program received;
stereophonic sound systems;
digital quality sound;
new services such as teletext;
ability to be adapted to HDTV (high-definition television) standards of television.
Advantages such as this require the following features in the tubes:
improvement in the size of the impact of the electron beams on the screen;
choice of substantially constant screen and mask pitches throughout the illuminated surface;
"cinemascope" format "wide" and "flat" screen with a ratio generally equal to 16/9;
good tolerance of the tube in terms of white and of color purity throughout the range of the intensities of electron beams;
good parameters of brilliance and contrast;
improvement of the anti-vibration characteristics of the mask (improved insensitivity to microphonic effects due, in particular, to shocks to the television set and to the vibrations produced by the loudspeakers of the television set).
In the prior art, the aesthetic quality of television tubes is gradually tending towards increasingly flat screens. One type of currently used "plane" front panel is called a "planar" front panel and is described in particular, in the U.S. Pat. Nos. 4,786,840 and 4,839,556. Tubes such as this work properly but require corrections to obtain good image geometry; these corrections cannot be obtained by the deflector alone.
Furthermore, the planeity of the screen has repercussions on the geometry of the mask and induces problems of thermomechanical behavior which take the form of doming and blister flaws.
A first object of the present invention is a method for the fabrication, for high-definition television, of a "wide" screen trichromatic tube (with a ratio of 16/9) but also capable of having the standard ratio 4/3, the screen of which is as flat as possible and requires the fewest possible geometrical corrections, a method that enables the making of a very wide range of tubes of very diverse dimensions and planeities, with the fabrication being done in the simplest possible way without using any cylindrical element in the illumination light box of the front panel.
Another object of the present invention is a trichromatic tube for high-definition television, in particular with a "wide" screen with a so-called "screen pitch" coefficient that is as constant as possible, the edges of the screen being as rectilinear as possible, the geometrical characteristics of the screen giving the linearity of the luminophor lines an optimal quality without the use of any cylindrical element in the illumination light box of the front panel, the performance characteristics of the tube being optimized with respect to the doming and blister coefficients, and of microphonic phenomena and with respect to the tolerance of purity of the colors.
The present invention proposes a method for the fabrication of a color television tube, comprising a glass envelope wherein there is included an electron gun in a neck and a shadow mask in front of an internal face of a screen front panel bearing luminophors, said method consisting in:
firstly, computing the internal area of the screen by a finite element method so that the screen pitch is substantially constant throughout the surface of the front panel;
then computing the mask matched with the front panel so that the mask pitch is substantially constant, if necessary in reiterating the computation of the internal surface area of the front panel;
computing the external surface area of the front panel by a finite element method so that the anti-implosion requirements relating to thickness and height of the skirt and the cost requirements of the front panel are achieved and,
imprinting the layers of phosphors on the internal surface without resorting to cylindrical elements in the illumination light box.